1. Field of the Invention
The present invention relates to a Plasma Display Panel (PDP) and, more particularly, to a PDP having an electrode structure which is advantageous in realizing higher density and high luminance display.
2. Description of the Related Art
A Plasma Display Panel (PDP) is a display element which realizes an image using visible light generated by exciting phosphors with Vacuum UltraViolet (VUV) light radiated by a plasma obtained by the discharge of gas. Such a PDP can realize an extra-large screen of over 60 inches with a thickness of no more than 10 cm. Since the PDP is a self-emitting display device as is a Cathode Ray Tube (CRT), it has good color reproduction and does not have a distortion phenomenon depending upon the viewing angle. Furthermore, the PDP has good productivity and low-manufacturing cost since it has a simple manufacturing method compared to that of a Liquid Crystal Display (LCD), etc. Thus, the PDP has been spotlighted as a next-generation industrial flat panel display and a home TV display.
The structure of a PDP has been developed over a long period of time since the 1970's. The most common structure is a three-electrode coplanar discharge structure. The three-electrode coplanar discharge type structure includes one substrate having two electrodes disposed on the same plane, and the other substrate, which is separated from the one substrate by a predetermined gap therebetween, and has address electrodes extending in a perpendicular direction. In the three-electrode coplanar discharge structure, a discharge gas is sealed between the two substrates.
A PDP employs a glow discharge so as to produce visible light, which is visible with the naked eyes. A glow discharge occurs when an excited gas is generated due to the collision of electrons and gases. Ultraviolet light rays are generated by the excited gas. Ultraviolet light rays collide with phosphors within discharge cells to generate visible light. The generated visible light passes through a front transparent substrate and then reaches the naked eyes. A significant amount of input power is lost through these steps.
Glow discharge is usually obtained by supplying a voltage higher than a discharge firing voltage between two electrodes under a low atmospheric pressure (<1 atm). The discharge firing voltage is a function defined by the type of gas, the atmospheric pressure and the distance between electrodes. For an AC discharge, a discharge firing voltage is influenced by the capacitance (the dielectric constant, the electrode area and the thickness) of a dielectric material and a frequency of the supplied voltage as well as the above three factors.
In order for discharging to begin, a significant high voltage is needed. Once a discharge has been generated, however, distribution of a voltage between the cathode and the anode has a distorted shape due to a difference in spatial charges generated in the vicinity of the cathode and the anode. Most of a voltage is consumed in the vicinity of two electrodes, i.e., in regions called a cathode sheath and an anode sheath. The amount of voltage consumed in a positive column region is relatively insignificant. More particularly, in a glow discharge generated in a PDP, it is known that a voltage consumed in the cathode sheath is significantly higher than that consumed in the anode sheath.
Visible light is emitted by the collision of ultraviolet light rays and the phosphors. Ultraviolet light rays are generated when the energy level of Xenon (Xe) changes from an excited state to a ground state. Xenon (Xe) in the excited state is produced by the collision of Xenon (Xe) in the ground state and electrons. Accordingly, in order to increase the ratio of generated visible light with respect to the input power, i.e., the emission efficiency, it is necessary to increase the electron heating efficiency.
The electron heating efficiency in the positive column region is generally higher than the electron heating efficiency in the cathode sheath region. Thus, the emission efficiency of a PDP can be improved by increasing the positive column region. Since thicknesses of the sheath regions are almost the same under the same pressure, it is necessary to increase the length of the discharge in order to increase the emission efficiency.
In a PDP having a three-electrode structure, the discharge occurs in a region where the distance between two electrodes is the smallest (i.e., a central portion of a discharge cell). The discharge then moves to the edge regions of the electrodes. The reason why the discharge is generated at the central region is that a discharge firing voltage in that region is low. The discharge firing voltage is a function of a multiplication of the pressure and the distance between electrodes. A PDP operating region is located at the right side in which the Paschen curve has a minimum value. Once the discharge is begun, it is maintained by a voltage that is significantly lower than the discharge firing voltage due to the formation of spatial charges. A voltage supplied between two electrodes gradually lowers as time goes by. After the discharge has occurred, as ions and electrons are accumulated in the central region, the intensity of an electric field weakens and the discharge in this region disappears.
A cathode spot and an anode spot move to a region where surface charges do not exist as time goes by, i.e., in the vicinity of electrode edges. Since a voltage supplied between two electrodes decreases as time goes by, a strong discharge is generated at the central region (a structure having a low emission efficiency) of a discharge cell, and a weak discharge is generated in the vicinity of discharge cell edges (a structure having a high emission efficiency). Due to this, an existing three-electrode coplanar discharge structure is inevitably low in the ratio of generated heat electrons with respect to input power. This results in a low emission efficiency.
In order to solve the above-mentioned problems of the three-electrode structure, the distance between display electrodes must be increased to cause a discharge firing voltage to increase.